Synthesis and Spinnability of the High Softening-point Polycarbosilane†

doi:10.7503/cjcu20140272

Abstract

Abstract:

Polycarbosilane(PCS) was synthesized by polydimethylsilane as starting material via high-temperature-normal-pressure method. The characteristics of polycondensation reaction and the increase mode of molecular weight were investigated by changing the reaction conditions. Moreover, the relationship between structure and spinnability of PCS was discussed. The results show that the condensation reaction of PCS at high temperature can occur in two different ways, the steady growth of molecular weight and the accelerated growth of molecular weight, corresponding to the polycondensation reaction between molecule of PCS with different molecular weights. The PCS obtained by steady growth pattern had a bimodal molecular weight distribution which possessed good spinnability. However, PCS formed by the accelerated growth model contained too much branching structures, which exhibited multi peak molecular weight distribution and poor spinnability. High softening-point PCS(256—287 ℃) with a number average molecular weight of 2.3×10³ and good spinnability was successful synthesized by polycontrolling the polycondensation reaction condition to make it progress in the steady growth model.

Key words: Synthesis of polycarbosilane, High softening-point, Spinnability, Polycondensation reaction

CLC Number:

O631

TrendMD:

LI Yongqiang, SONG Yongcai. Synthesis and Spinnability of the High Softening-point Polycarbosilane^†[J]. Chem. J. Chinese Universities, 2014, 35(10): 2272.

Figures/Tables 10

Table 1 Characteristics of PCS synthesized in different conditions

Sample	Reaction temperature/℃	Holding time/h	Softening point/℃	10^-3 $M ˉ n$	PDI^*	Yield(%)	Insoluble residue(%)
PCS-1	440	4	165—186	1.5	2.47	33.2	2.53
PCS-2	450	4	186—211	1.7	2.71	39.3	2.44
PCS-3	460	4	205—237	1.9	2.84	40.9	2.17
PCS-4	470	4	265	2.3	4.84	41.9	2.38
PCS-5	480	4	>300	4.8	6.02	15.2	41.82
PCS-6	450	6	194—224	1.8	2.96	41.7	2.39
PCS-7	450	8	209—242	1.9	3.22	42.0	2.40
PCS-8	450	12	229—263	2.1	3.70	46.7	2.43
PCS-9	450	16	256—287	2.3	4.09	48.6	2.42
PCS-10	450	24	>300	2.7	5.30	51.8	2.64

Table 1 Characteristics of PCS synthesized in different conditions

Sample	Reaction temperature/℃	Holding time/h	Softening point/℃	10^-3 $M ˉ n$	PDI^*	Yield(%)	Insoluble residue(%)
PCS-1	440	4	165—186	1.5	2.47	33.2	2.53
PCS-2	450	4	186—211	1.7	2.71	39.3	2.44
PCS-3	460	4	205—237	1.9	2.84	40.9	2.17
PCS-4	470	4	265	2.3	4.84	41.9	2.38
PCS-5	480	4	>300	4.8	6.02	15.2	41.82
PCS-6	450	6	194—224	1.8	2.96	41.7	2.39
PCS-7	450	8	209—242	1.9	3.22	42.0	2.40
PCS-8	450	12	229—263	2.1	3.70	46.7	2.43
PCS-9	450	16	256—287	2.3	4.09	48.6	2.42
PCS-10	450	24	>300	2.7	5.30	51.8	2.64

Fig.1 GPC curves of PCS synthesized in different conditions (A) Reaction under different temperature for 4 h. a. 440 ℃; b. 450 ℃; c. 460 ℃; d. 470 ℃; e. 480 ℃. (B) Reaction under 450 ℃ for different holding time. a. 4 h; b. 6 h; c. 8 h; d. 12 h; e. 16 h; f. 24 h.

Fig.2 Influence of reaction conditions on Mˉn (A) Reaction time: 4 h; (B) reaction temperature: 450 ℃.

Scheme 1 Model of condensation reaction between PCS molecule

Fig.3 Influence of reaction conditions on contents of MH(a), MM(b) and ML(c) of PCS (A) Reaction time: 4 h; (B) reaction temperature: 450 ℃.

Fig.4 1H NMR(A) and 29Si NMR(B) spectra of KD-PCS(a), PCS-4(b) and PCS-9(c)

Fig.5 FTIR spectra of KD-PCS(a), PCS-4(b) nd PCS-9(c)

Fig.6 Influence of reaction conditions on ASi—H/ASi—CH3(a) and ASi—CH2—Si/ASi—CH3(b) (A) Reaction under different temperature for 4 h; (B) reaction under 450 ℃ for different holding time.

Table 2 Melting spinning conditions and spinnability of PCS

Sample	$T a *$ /℃	Temperature/℃	Pressure/MPa	Spin-speed/(r·min^-1)	Continuous time/min	Diameter/μm	Spinnability
PCS-1	165	305	0.5	350	>30	14.9	Very good
PCS-2	186	326	0.5	350	>30	15.2	Very good
PCS-3	205	345	0.5	350	>30	15.4	Very good
PCS-4	265	405	0.7	200	<1	17.2	Unspinnable
PCS-6	194	335	0.5	350	>30	15.6	Very good
PCS-7	209	350	0.5	350	>30	15.3	Very good
PCS-8	229	370	0.5	300	27	16.2	Good
PCS-9	256	400	0.5	350	17	14.8	Good
PCS-9	256	400	0.5	450	8	10.6	Good

Table 2 Melting spinning conditions and spinnability of PCS

Sample	$T a *$ /℃	Temperature/℃	Pressure/MPa	Spin-speed/(r·min^-1)	Continuous time/min	Diameter/μm	Spinnability
PCS-1	165	305	0.5	350	>30	14.9	Very good
PCS-2	186	326	0.5	350	>30	15.2	Very good
PCS-3	205	345	0.5	350	>30	15.4	Very good
PCS-4	265	405	0.7	200	<1	17.2	Unspinnable
PCS-6	194	335	0.5	350	>30	15.6	Very good
PCS-7	209	350	0.5	350	>30	15.3	Very good
PCS-8	229	370	0.5	300	27	16.2	Good
PCS-9	256	400	0.5	350	17	14.8	Good
PCS-9	256	400	0.5	450	8	10.6	Good

Fig.7 SEM images of the surface(A) and cross sections[insets of (A) and (B)] PCS-9 fibers span at different winding speeds of 350 r/min(A) and 450 r/min(B)

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