Phase Behavior and Conformational Asymmetry near the Comb-to-Bottlebrush Transition in Linear-Brush Block Copolymers

This study explores how conformational asymmetry influences the bulk phase behavior of linear-brush block copolymers. We synthesized 60 diblock copolymers composed of poly(trifluoroethyl methacrylate) as the linear block and poly[oligo(ethylene glycol) methyl ether methacrylate] as the brush block, varying the molecular weight, composition, and side-chain length to introduce different degrees of conformational asymmetry. Using small-angle X-ray scattering, we determined the morphology and phase diagrams for three different side-chain length systems, mainly observing lamellar and cylindrical phases. Increasing the side-chain length of the brush block from three to nine ethylene oxide units introduces sufficient asymmetry between the blocks to alter the phase behavior, shifting the lamellar-to-cylindrical transitions toward lower brush block compositions and transitioning the brush block from the dense comb-like regime to the bottlebrush regime. Coarse-grained simulations support our experimental observations and provide a mapping between the composition and conformational asymmetry. A comparison of our findings to strong stretching theory across multiple phase boundary predictions confirms the transition between the dense comb-like regime and the bottlebrush regime.

c Calculated from the molar ratios obtained by 1 H NMR and based on the Mn first calculated by SEC for PTFEMA.where Mw TFEMA and Mw OEM9 are the molar mass of TFEMA and OEM9 units, 168.11 g mol -1 and 500 g mol -1 , respectively.
c Calculated from the molar ratios obtained by 1 H NMR and based on the Mn first calculated by SEC for PTFEMA.

Density estimation by the van Krevelen group contribution method
Densities for the POEMx segments were estimated from: where M is the average molecular weight of the repeat unit (232.27g mol -1 , g mol -1 , 300 g mol -1 and 500 g mol -1 for OEM3, OEM5 and OEM9, respectively) and   is the standard molecular volume at room temperature for a rubbery amorphous polymer.The   values for each polymer were predicted from the expression below by using the Krevelen group contributions values listed in Table S5. 6,7  (298 K) = ∑   (298 K)

Parameters setting for SCFT from experimental data
The total degree of polymerization was rescaled as input for the SCFT (denoted as   ) according to the following expressions: where   is the reference volume (118 Å 3 ), and  is the segment molecular volume defined as: where N' is the number of repeat units in the segment, M is the segment number average molecular weight,  0 is the molecular weight of the corresponding repeat unit (168.11g mol -1 , 232.27 g mol -1 , g mol -1 , 300 g mol -1 and 500 g mol -1 for TFEMA, OEM3, OEM5 and OEM9, respectively), ρ is the segment density (1.45 g cm -3 , 1.17 g cm -3 , 1.16 g cm -3 , 1.13 g cm -3 for PTFEMA, POEM3, POEM5 and POEM9, respectively), and   is the Avogadro's number.
c Determined by SAXS.

Figure S1 .
Figure S1.SEC traces of the full set of PTFEMA homopolymers.Mn values ranged from 5.2 kg mol -1 to 24.7 kg mol -1 .

Figure S2 .
Figure S2.RAFT polymerization of TFEMA using AIBN as initiator and CPBD as chain transfer agent.(a) Evolution of experimental Mn and Đ as function of monomer conversion.(b) ln([M]0/[M]) as function of reaction time, with [M]0 and [M] being the concentrations of monomers at time zero and t, respectively.

*
POEMx determined using Krevelen group contribution.Vr was predicted considering 4.5 EO units in the repeat unit; for practical reasons we referred to this monomer as OEM5 through all the text.

b−POEM3 Entry # PTFEMA Mn a (kg mol -1 ) Reaction time (h) x TFEMA b Mn c (kg mol -1 ) Đ a
a Determined by SEC in THF using PS standards.
a Determined by SEC in THF using PS standards.bCalculated from the molar ratios obtained by

N PTFEMA b N POEM3 b N Total b f POEM3 b Morphology
Calculated from the molar ratio of both blocks determined by 1 H NMR. a

N PTFEMA b N POEM5 b N Total b f POEM5 b Morphology c
a Calculated from the molar ratio of both blocks determined by 1 H NMR.

Table S9 .
Simulation systems listed by side-chain length and minimum and maximum fB via bottlebrush scaling.

Table S10 .
Simulation systems listed by side-chain length and minimum and maximum fB via comb scaling.