Influences of Topological Chain Structures to the Crystallization of Block Copolymers†

doi:10.7503/cjcu20150237

Abstract

Abstract:

The crystallization behavior of two kinds of triblock block copolymers synthesized with equal content of polyethylene glycol(PEG) and almost equal content of polystyrene(PS), namely H-type(PS)₂-PEG-(PS)₂(PEG chains linking in the middle of PS chains) and linear PS-PEG-PS(PEG chains linking to the end of PS chains), were studied comparatively by small-angle X-ray scattering(SAXS), wide angle X-ray diffraction(WAXD), differential scanning calorimetry(DSC), polarized optical microscopy(POM) and other means. It is found that, although the crystal forms of PEGs in copolymers are same, the crystallization tem-perature of the H-type is lower than that of the linear, the thickness of PEG crystal lamella is smaller, and the crystallization rate is slower at the same temperature, which originates from the larger steric hindrance caused by the bifurcation chain structure of H-type copolymer.

Key words: Block copolymer, Crystallization behavior, Dynamics, Polyehylene glycol, Polystyrene

CLC Number:

O631

TrendMD:

ZHANG Lili, CHEN Qiaoyue, ZHOU Hengwei, SHI Tongfei, HUANG Yineng. Influences of Topological Chain Structures to the Crystallization of Block Copolymers^†[J]. Chem. J. Chinese Universities, 2015, 36(9): 1832.

Figures/Tables 9

Table 1 Basic characteristics of LTC and HTC samples

Sample	Architecture	Chain	Peak area of a+b	Peak area of c	M_totoal	PDI
LTC		PS₁₅PEG₂₂₇PS₁₅	16.760	100	13120	1.2
HTC		(PS₇)₂PEG₂₂₇(PS₇)₂	16.408	100	12912	1.1

Fig.1 1H NMR spectra of LTC(a) and HTC(b) samples

Fig.2 Standard DSC cooling(a, b) and heating(a', b') scans of LTC(a, a') and HTC(b, b') samples

Table 2 Crystallization and melting temperatures for LTC and HTC samples instandard DSC scans

Sample	f_PEG(%)	$T c, PEG$ /℃	ΔH_c/(J·g^-1)	$T m, PEG$ /℃	ΔH_m/(J·g^-1)	X_c(%)
LTC	76.2	18.4	94.28	56.0	107.80	68.0
HTC	77.4	8.2	79.18	54.4	98.01	60.8

Table 2 Crystallization and melting temperatures for LTC and HTC samples instandard DSC scans

Sample	f_PEG(%)	$T c, PEG$ /℃	ΔH_c/(J·g^-1)	$T m, PEG$ /℃	ΔH_m/(J·g^-1)	X_c(%)
LTC	76.2	18.4	94.28	56.0	107.80	68.0
HTC	77.4	8.2	79.18	54.4	98.01	60.8

Fig.3 Variation in the spherulite radius with the crystallization time for LTC(A) and HTC(B) samples at different crystallization temperatures

Table 3 Spherulitic growth rates from POM and crystallization rates from DSC for LTC and HTC samples

T_c/℃	Growth rate/(μm·min^-1)		Grystallization rate/min^-1		T_c/℃	Growth rate/(μm·min^-1)		Grystallization rate/min^-1
T_c/℃	LTC	HTC		LTC	HTC	LTC	HTC	LTC	HTC
33	56.16	53.65			38	33.78	30.51	0.056	0.045
34	54.76	48.82			39			0.048	0.033
35		44.31			40			0.042	0.043
36	45.49	41.02			41			0.030	0.028
37	40.70	35.55	0.052

Fig.4 WAXD patterns of LTC(a) and HTC(b) samples after isothermal crystallization at 38 ℃

Fig.5 One dimensional electron density correlation function K(Z) of LTC(a) and HTC(b) samples after isothermal crystallization at 38 ℃ vs. the length(Z) along the normal direction of the lamella(A) and scattering intensity square(Is2) vs. the scattering vector(s)(B)L: Long period; L2: crystal lamellar thickness; L1: noncrystal lamellar thickness.

Fig.6 Lamellar parameters(L, L1 and L2) vs. temperature for LTC and HTC

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