Low modulus, high elasticity and high peel adhesion acrylate pressure sensitive adhesives

doi:10.11949/0438-1157.20230381

Abstract

Abstract:

Acrylate pressure sensitive adhesives are widely used in the assembly of electronic devices. With the development of flexible electronics such as foldable phone, traditional pressure sensitive adhesives fail to meet the needs of flexible electronics for repeated deformation due to the trade-off effect among low modulus, high elasticity and high peel adhesion. The poly(styrene-b-2-ethylhexyl acrylate-b-styrene) (SEHAS) and poly(styrene-b-2-ethylhexyl acrylate) (SEHA) copolymers of styrene and 2-ethylhexyl acrylate were prepared by design via RAFT emulsion polymerization. The mechanical properties, viscoelasticity and adhesion properties of SEHAS/SEHA blends were studied. By adjusting the blending ratio of SEHAS/SEHA from 100/0 to 25/75, it was found that the glass transition temperature remained unchanged at -68℃, the shear storage modulus decreased from 27 kPa to 15 kPa, the peel strength increased from 8.1 N/25 mm to 10.3 N/25 mm, and the strain recovery ratio remained above 95%. SEHAS/SEHA blending turns out to be a new and facile method to significantly reduce the modulus while maintain the integrality of a network and improve viscoelasticity. Thus, very soft pressure sensitive adhesives with good elasticity and adhesion can achieve.

Key words: RAFT emulsion polymerization, block copolymer, pressure sensitive adhesive, elastomer, electronic materials, elasticity, composites

摘要：

丙烯酸酯压敏胶广泛应用在电子器件的装配中。随着可折叠屏手机等柔性电子器件发展，传统压敏胶因无法平衡低模量、高弹性以及高剥离强度而难以满足柔性电子器件对反复动态变形的需求。以苯乙烯、丙烯酸异辛酯为单体，采用RAFT乳液聚合设计制备了聚苯乙烯-b-聚丙烯酸异辛酯-b-聚苯乙烯（SEHAS）和聚苯乙烯-b-聚丙烯酸异辛酯（SEHA）嵌段聚合物，研究两种嵌段共聚物共混体系的力学性能、黏弹性和黏结性能。发现当共混物中SEHA的含量从0（质量）提高到75%（质量）时，玻璃化温度仍为-68℃，保持不变，剪切储能模量从27 kPa下降至15 kPa，剥离强度从8.1 N/25 mm提升到10.3 N/25 mm，应变回复率仍然保持在95%以上。研究表明SEHAS/SEHA共组装是一种简便降低模量同时维持较好的交联网络完整性并提高黏弹性的新方法，能够更好地平衡压敏胶高柔性、大变形后的回弹性和良好界面黏合性之间的关系。

关键词: RAFT乳液聚合, 嵌段共聚物, 压敏胶, 弹性体, 电子材料, 弹性, 复合材料

CLC Number:

TQ 436.3

Ao ZHANG, Yingwu LUO. Low modulus, high elasticity and high peel adhesion acrylate pressure sensitive adhesives[J]. CIESC Journal, 2023, 74(7): 3079-3092.

张澳, 罗英武. 低模量、高弹性、高剥离强度丙烯酸酯压敏胶[J]. 化工学报, 2023, 74(7): 3079-3092.

Figures/Tables 20

Fig.1 1H NMR spectra of macro-RAFT

Fig.2 GPC curves of chain extensions during the synthesis of the block polymers

Table 1 Molecular structure of the block copolymers

Type	Stage	$x$ /%	M_n,design^①	M_n,exp^②	PDI
SEHAS	1	96.9	15	17.4	1.27
	2	97.1	195	201.6	2.08
	3	95.5	210	217.1	2.10
SEHA	1	96.8	5	6.3	1.64
SEHA	2	97.6	125	124.0	2.74

Table 1 Molecular structure of the block copolymers

Type	Stage	$x$ /%	M_n,design^①	M_n,exp^②	PDI
SEHAS	1	96.9	15	17.4	1.27
	2	97.1	195	201.6	2.08
	3	95.5	210	217.1	2.10
SEHA	1	96.8	5	6.3	1.64
SEHA	2	97.6	125	124.0	2.74

Fig.3 The Fourier transform infrared(FTIR) spectra of SEHA and SEHA

Fig.4 1H NMR spectra of SEHAS and SEHA

Fig.5 DSC curves of SEHAS/SEHA with different blending ratios

Fig.6 AFM phase images of SEHAS/SEHA with different blending ratios

Fig.7 DMA curves of SEHAS/SEHA with different blending ratios

Fig.8 Tensile properties of SEHAS/SEHA with different blending ratios

Fig.9 Differential modulus as a function of strain of SEHAS/SEHA with different blending ratios

Fig.10 Relationship between elastic modulus and SEHA content

Fig.11 Schematic of SEHAS and SEHAS/SEHA structure

Fig.12 Rheology of SEHAS/SEHA with different blending ratios

Fig.13 Tack curves of SEHAS/SEHA with different blending ratios

Fig.14 Peel adhesion of SEHAS/SEHA with different blending ratios

Fig.15 Stress and strain related with time of SEHAS/SEHA with different blending ratios under a strain of 200%, 300% and 400%

Fig.16 Stress relaxation ratio and strain recovery ratio of SEHAS/SEHA with different blending ratios under a strain of 200%, 300% and 400%

Fig.17 Experimental (dot) and fitting results (solid line) with KWW equation of stress relaxation behavior of SEHAS/SEHA with different blending ratios under a strain 400%

Table 2 Fitting parameters of SEHAS/SEHA with different blending ratios under a strain of 400%

SEHAS/SEHA比例	$σ r$ /MPa	$σ p$ /MPa	$τ$ /min	$β$
100∶0	0.033	0.095	3.21	0.35
75∶25	0.034	0.082	2.20	0.32
50∶50	0.045	0.061	2.45	0.34
25∶75	0.022	0.036	0.84	0.34

Table 2 Fitting parameters of SEHAS/SEHA with different blending ratios under a strain of 400%

SEHAS/SEHA比例	$σ r$ /MPa	$σ p$ /MPa	$τ$ /min	$β$
100∶0	0.033	0.095	3.21	0.35
75∶25	0.034	0.082	2.20	0.32
50∶50	0.045	0.061	2.45	0.34
25∶75	0.022	0.036	0.84	0.34

Table 3 The property and performance comparison of the foldable pressure sensitive adhesive between the current work and the literature

品牌/参数	膜厚/μm	断裂伸长率/%	玻璃化温度/°C	剪切储能模量 (1 rad/s)/kPa	损耗因子 (1 rad/s)	应力松弛率/%	应变回复率/%	剥离强度/ (N/25 mm)
SEHAS∶SEHA=100∶0	25	1000	-68	27	0.21	约20	>95	8.1
SEHAS∶SEHA=25∶75	25	700	-68	15	0.30	约40	>95	10.3
3M CEF3501	25	598	-42	30	0.33	—	—	8.5
AA改性^[10]	100	约410	-54	27	—	约48	>95	约13.8^①
丙烯酸酯弹性体改性^[18]	75	—	-40	—	—	约50	约75	约12.0^①
交联密度调控^[16]	50	—	-31	—	—	约71	约71	约10.0^①

References 37

1	Wang C, Hwang D, Yu Z B, et al. User-interactive electronic skin for instantaneous pressure visualization[J]. Nature Materials, 2013, 12(10): 899-904.
2	Park J, Heo S, Park K, et al. Research on flexible display at Ulsan National Institute of Science and Technology[J]. NPJ Flexible Electronics, 2017, 1: 9.
3	Rogers J A, Someya T, Huang Y G. Materials and mechanics for stretchable electronics[J]. Science, 2010, 327(5973): 1603-1607.
4	Lim D, Baek M J, Kim H S, et al. Carboxyethyl acrylate incorporated optically clear adhesives with outstanding adhesion strength and immediate strain recoverability for stretchable electronics[J]. Chemical Engineering Journal, 2022, 437: 135390.
5	Zhang P, Zhou W Y, He Y F, et al. Stretchable heterogeneous polymer networks of high adhesion and low hysteresis[J]. ACS Applied Materials & Interfaces, 2022, 14(43): 49264-49273.
6	Kim S, An J, Son S R, et al. Fabrication of highly elastic and optically transparent adhesive films for flexible displays using multifunctional photocrosslinker[J]. Molecular Crystals and Liquid Crystals, 2022, 740(1): 28-34.
7	Bartkowiak M, Czech Z, Mozelewska K, et al. Influence of thermal reactive crosslinking agents on the tack, peel adhesion, and shear strength of acrylic pressure-sensitive adhesives[J]. Polymer Testing, 2020, 90: 106603.
8	Baek S S, Jang S J, Hwang S H. The effect of crosslinker type on adhesion properties of transparent acrylic pressure sensitive adhesives for optical applications[J]. Elastomers and Composites, 2014, 49(3): 199-203.
9	Zhang X W, Ding Y T, Zhang G L, et al. Preparation and rheological studies on the solvent based acrylic pressure sensitive adhesives with different crosslinking density[J]. International Journal of Adhesion and Adhesives, 2011, 31(7): 760-766.
10	Lee J H, Park J, Myung M H, et al. Stretchable and recoverable acrylate-based pressure sensitive adhesives with high adhesion performance, optical clarity, and metal corrosion resistance[J]. Chemical Engineering Journal, 2021, 406: 126800.
11	Lee S H, You R, Yoon Y I, et al. Preparation and characterization of acrylic pressure-sensitive adhesives based on UV and heat curing systems[J]. International Journal of Adhesion and Adhesives, 2017, 75: 190-195.
12	Czech Z, Kabatc J, Kowalczyk A, et al. Application of selected 2-methylbenzothiazoles AS cationic photoreactive crosslinkers for pressure-sensitive adhesives based on acrylics[J]. International Journal of Adhesion and Adhesives, 2015, 58: 1-6.
13	Kim J S, Kim H J, Kim Y D. Flexibility properties of pressure-sensitive adhesive with different pattern of crosslinking density for electronic displays[J]. Journal of Materials Research and Technology, 2021, 15: 1408-1415.
14	Back J H, Baek D, Sim K B, et al. Optimization of recovery and relaxation of acrylic pressure-sensitive adhesives by using UV patterning for flexible displays[J]. Industrial & Engineering Chemistry Research, 2019, 58(10): 4331-4340.
15	Mao J, Li T F, Luo Y W. Significantly improved electromechanical performance of dielectric elastomers via alkyl side-chain engineering[J]. Journal of Materials Chemistry C, 2017, 5(27): 6834-6841.
16	Lee J H, Lee T H, Shim K S, et al. Effect of crosslinking density on adhesion performance and flexibility properties of acrylic pressure sensitive adhesives for flexible display applications[J]. International Journal of Adhesion and Adhesives, 2017, 74: 137-143.
17	Lee J H, Lee T H, Shim K S, et al. Molecular weight and crosslinking on the adhesion performance and flexibility of acrylic PSAs[J]. Journal of Adhesion Science and Technology, 2016, 30(21): 2316-2328.
18	Lee J H, Shim G S, Kim H J, et al. Adhesion performance and recovery of acrylic PSA with acrylic elastomer (AE) blends via thermal crosslinking for application in flexible displays[J]. Polymers, 2019, 11(12): 1959.
19	Bartkowiak M, Czech Z, Kim H J, et al. Photoreactive UV-crosslinkable acrylic pressure-sensitive adhesives (PSA) containing multifunctional photoinitiators[J]. Polymers, 2021, 13(24): 4413.
20	Chen Z Q, Xiao Y H, Fang J W, et al. Ultrasoft-yet-strong pentablock copolymer as dielectric elastomer highly responsive to low voltages[J]. Chemical Engineering Journal, 2021, 405: 126634.
21	徐菘. RAFT乳液聚合可控制备SBAS新型水性压敏胶[D]. 杭州: 浙江大学, 2015.
	Xu S. Development of novel water-based high performance pressure-sensitive adhesive of SBAS via RAFT emulsion polymerization[D]. Hangzhou: Zhejiang University, 2015.
22	Ferguson C J, Hughes R J, Nguyen D, et al. Ab initio emulsion polymerization by RAFT-controlled self-assembly[J]. Macromolecules, 2005, 38(6): 2191-2204.
23	Wang X G, Luo Y W, Li B G, et al. Ab initio batch emulsion RAFT polymerization of styrene mediated by poly(acrylic acid-b-styrene) trithiocarbonate[J]. Macromolecules, 2009, 42(17): 6414-6421.
24	Ma Z P, Xie Y H, Mao J E, et al. Thermoplastic dielectric elastomer of triblock copolymer with high electromechanical performance[J]. Macromolecular Rapid Communications, 2017, 38(16): 1700268.
25	Wu L F, Cochran E W, Lodge T P, et al. Consequences of block number on the order-disorder transition and viscoelastic properties of linear (AB) _n multiblock copolymers[J]. Macromolecules, 2004, 37(9): 3360-3368.
26	Guo Y L, Gao X A, Luo Y W. Suppressing the long-chain branching in the synthesis of poly(styrene-b-butyl acrylate-b-styrene) in RAFT emulsion polymerization by tuning the interfacial properties[J]. Journal of Polymer Science Part A: Polymer Chemistry, 2015, 53(12): 1464-1473.
27	Hadjichristidis N, Pispas S, Floudas G. Block Copolymers: Synthetic Strategies, Physical Properties, and Applications[M]. Hoboken, NJ: Wiley, 2003.
28	Swann J M G, Topham P D. Design and application of nanoscale actuators using block-copolymers[J]. Polymers, 2010, 2(4): 454-469.
29	Fang Y, Xia J. Highly stretchable, soft, and clear viscoelastic film with good recoverability for flexible display[J]. ACS Applied Materials & Interfaces, 2022, 14(33): 38398-38408.
30	高扬. 纳米BaTiO₃增强丙烯酸酯嵌段共聚物介电弹性体机电性能[D]. 杭州: 浙江大学, 2021.
	Gao Y. Mechanical and electrical properties of acrylate block copolymer dielectric elastomer reinforced by nano BaTiO₃ [D]. Hangzhou: Zhejiang University, 2021.
31	冒杰. 介电弹性体新材料与纤维状驱动器的设计与可控制备[D]. 杭州: 浙江大学, 2020.
	Mao J. Design and controllable preparation of dielectric elastomer materials and fibrous actuators[D]. Hangzhou: Zhejiang University, 2020.
32	Roos A, Creton C. Effect of the presence of diblock copolymer on the nonlinear elastic and viscoelastic properties of elastomeric triblock copolymers[J]. Macromolecules, 2005, 38(18): 7807-7818.
33	Ha M H, Choi J K, Park B M, et al. Highly flexible cover window using ultra-thin glass for foldable displays[J]. Journal of Mechanical Science and Technology, 2021, 35(2): 661-668.
34	Tong J D, Jerôme R. Dependence of the ultimate tensile strength of thermoplastic elastomers of the triblock type on the molecular weight between chain entanglements of the central block[J]. Macromolecules, 2000, 33(5): 1479-1481.
35	Sakaguchi Y, Kosaka N, Hori N, et al. Rheological analysis of the adhesion surface with a scanning probe microscope (SPM)[J]. International Journal of Adhesion and Adhesives, 2011, 31(1): 1-8.
36	Fujita M, Takemura A, Ono H, et al. Effects of miscibility and viscoelasticity on shear creep resistance of natural-rubber-based pressure-sensitive adhesives[J]. Journal of Applied Polymer Science, 2000, 75(12): 1535-1545.
37	Fujita M, Kajiyama M, Takemura A, et al. Effects of miscibility on probe tack of natural-rubber-based pressure-sensitive adhesives[J]. Journal of Applied Polymer Science, 1998, 70(4): 771-776.

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