Effect of soft segment structure on properties of polyurethane elastomers

doi:10.11949/0438-1157.20190477

Abstract

Abstract:

Using four different soft segments, i.e. polyterahydrofuran diol (PTMG), polycaprolactone diol (PCL), hydroxyl-terminated polybutadiene with high cis-1,4 content (HTPB), and commercial hydroxyl-terminated polybutadiene produced by free radical polymerization (FHTPB), four kinds of polyurethane elastomers (PUE) were prepared by a two-step solution polymerization. The effects of soft segment structure on mechanical properties and thermal properties at room temperature and low temperature were investigated by tensile test, dynamic mechanical property analysis (DMA), differential scanning calorimetry (DSC) and thermogravimetric analysis. It has been found that the tensile strength and elongation at break of the four PUEs at low temperature (-30℃) are superior to those at room temperature. This is not only related to the autofrettage effect induced by crystallization of soft segment at low temperature, but also to the increase of the degree of micro-phase separation between the soft and hard segments. Compared with the other three kinds of PUE, the soft segment in HTPB-PUE has lowest polarity and glass transition temperature (T _g), so the micro-phase separation is in highest degree, and the elastomer has the most excellent flexibility. Even at -30℃, elongation at break of the HTPB-PUE is up to 660%. PCL-PUE and PTMG-PUE are rigid because their soft segments are easy to crystallize and their degree of micro-phase separation between soft and hard segment is low. The cyclic tensile testing indicated that HTPB-PUE and FHTPB-PUE still have excellent elasticity at -30℃. The results from DSC and DMA showed that the T _g of HTPB-PUE is much lower than the other three PUEs, and the value from DSC is about -103℃. The initial thermal decomposition temperatures of the four PUEs are very similar, and are all around 270℃.

Key words: polyurethane, elastomer, soft segment, structure, properties

摘要：

分别以聚四氢呋喃二醇(PTMG)、聚己内酯二醇(PCL)、高顺式端羟基聚丁二烯(HTPB)和自由基聚合制得的端羟基聚丁二烯(FHTPB)为软段，采用溶液聚合两步法制得了四种聚氨酯弹性体(PUE)。通过拉伸试验、动态力学性能分析(DMA)、差示扫描量热(DSC)和热重分析等手段，考察了软段结构对它们室温及低温下力学性能、热性能等的影响。结果表明，四种PUE低温(-30℃)下的拉伸强度和断裂伸长率均大于室温下的对应值。这不仅与低温下软段诱导结晶所产生的自增强效应有关，也与软、硬两段的微相分离程度增大有关。相较于其他三种PUE，HTPB-PUE软段不仅玻璃化温度(T _g)最低，而且极性也最弱，因而微相分离程度高，具有优异的柔性，-30℃下其断裂伸长率仍达660%以上。PCL-PUE和PTMG-PUE因软段易结晶，且软段与硬段的微相分离程度低，则刚性强。低温循环拉伸试验表明，-30℃下HTPB-PUE和FHTPB-PUE有较强的弹性恢复能力，而PCL-PUE和PTMG-PUE则相对较差。DSC和DMA结果显示HTPB-PUE的T _g远低于其他三种PUE，其T _g(DSC)低至-103℃。此外，四种PUE的初始分解温度十分相近，均在270℃左右。

关键词: 聚氨酯, 弹性体, 软段, 结构, 性能

CLC Number:

TQ 323.8

Congcong ZHANG, Mengkai ZHENG, Bo-Geng LI. Effect of soft segment structure on properties of polyurethane elastomers[J]. CIESC Journal, 2019, 70(10): 4043-4051.

张聪聪, 郑梦凯, 李伯耿. 软段结构对聚氨酯弹性体性能的影响[J]. 化工学报, 2019, 70(10): 4043-4051.

Figures/Tables 10

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Sample	M _n/(g/mol)		Micro structure/%(mol)^③
Sample	GPC (PDI)^①	NMR^②	cis-1,4/trans-1,4/1,2-vinyl
PTMG	4820 (1.97)	2232	—
PCL	3480 (1.26)	1770	—
FHTPB	4790 (2.64)	2261	22/60/18
HTPB	4530 (2.24)	1996	96/1/3

Sample	M _n/(g/mol)		Micro structure/%(mol)^③
Sample	GPC (PDI)^①	NMR^②	cis-1,4/trans-1,4/1,2-vinyl
PTMG	4820 (1.97)	2232	—
PCL	3480 (1.26)	1770	—
FHTPB	4790 (2.64)	2261	22/60/18
HTPB	4530 (2.24)	1996	96/1/3

Sample	Soft segment	Shore A hardness	Young’s modulus/MPa		Tensile strength/MPa		Elongation at break/%		Tensile stress at 100%/MPa
Sample	Soft segment	Shore A hardness	25℃	-30℃	25℃	-30℃	25℃	-30℃	25℃	-30℃
PTMG-PUE	PTMG	68	16.6	40.0	6.30	42	272	486	4.40	16.05
PCL-PUE	PCL	85	51.2	142.0	11.80	49	234	458	9.12	24.91
FHTPB-PUE	FHTPB	68	8.6	11.2	4.17	16	184	480	3.43	5.41
HTPB-PUE	HTPB	65	6.0	7.7	4.93	23	341	668	3.21	4.45

Sample	Soft segment	Shore A hardness	Young’s modulus/MPa		Tensile strength/MPa		Elongation at break/%		Tensile stress at 100%/MPa
Sample	Soft segment	Shore A hardness	25℃	-30℃	25℃	-30℃	25℃	-30℃	25℃	-30℃
PTMG-PUE	PTMG	68	16.6	40.0	6.30	42	272	486	4.40	16.05
PCL-PUE	PCL	85	51.2	142.0	11.80	49	234	458	9.12	24.91
FHTPB-PUE	FHTPB	68	8.6	11.2	4.17	16	184	480	3.43	5.41
HTPB-PUE	HTPB	65	6.0	7.7	4.93	23	341	668	3.21	4.45

Sample	Soft segment	Storage modulus/MPa		T _g(PUE)^①/℃	T _g(PUE)^②/℃	T _g(polyol)^②/℃	ΔT _g ^③/℃
Sample	Soft segment	25℃	-100℃	T _g(PUE)^①/℃	T _g(PUE)^②/℃	T _g(polyol)^②/℃	ΔT _g ^③/℃
PTMG-PUE	PTMG	35.16	2558	-58.7	-70.7	-85.0	14.3
PCL-PUE	PCL	84.78	3219	-29.8	-43.3	-72.0	28.7
FHTPB-PUE	FHTPB	20.10	2639	-60.4	-82.2	-86.3	4.1
HTPB-PUE	HTPB	10.70	1196	-93.6	-103.3	-104.8	1.5